Corticomotor and somatosensory evoked potential evaluation of acute spinal cord injury in the rat.

Somatosensory evoked potentials (SSEPs) and corticomotor evoked potentials (CMEPs) were utilized to study acute blunt spinal cord trauma. Rats, anesthetized with ketamine hydrochloride, were subjected to a parasagittal craniotomy and a midthoracic laminectomy. SSEPs were cortically recorded and CMEPs were transcortically produced using epidural ball and disc electrodes. SSEPs were elicited and CMEPs were recorded via hindlimb percutaneous needle electrodes. After control records were made, animals were subjected to a 25-, 50-, or 75-g/cm impact to the dorsal cord surface via a modified weight drop procedure. Evaluation of neurological injury was made by SSEP and CMEP analysis as well as by physical testing with noxious stimulation applied to the hindlimb. Neurohistopathological verification of each spinal cord lesion was performed. No significant change in SSEP configuration was identified in animals subjected to a 25-g/cm cord impact; however, a small decrement in CMEP amplitude was consistently observed. Although vocalization to noxious stimulation was present, flexion activity was less than normal. Animals subjected to a 50-g/cm cord impact also showed no change in SSEP wave forms. All components of the CMEP were greatly attenuated with this injury. Either very weak movement or no movement to noxious stimulation was present without vocalization. After a 75-g/cm cord impact, both SSEPs and CMEPs were abolished. There was no movement or vocalization in response to noxious stimulation. Serial sections of the spinal cords revealed incremental destruction with increasing severity of injury. These results support the hypothesis that CMEPs are a more sensitive indicator of residual spinal cord function after injury than are SSEPs.